A unified communications (UC) system generally refers to a system that provides users with an integration of communications services. Users typically connect to the UC system through a single client to access the integrated communications services. The integrated communications services may include real-time services, such as instant messaging (IM), presence notifications, telephony, and video conferencing, as well as non-real-time services, such as email, SMS, fax, and voicemail.
Organizations, such as corporations, businesses, educational institutions, and government entities, often employ UC systems to enable internal communication among its members in a uniform and generally cost-efficient manner. In addition, organizations may employ UC systems for communicating with trusted external entities.
Currently, a number of third-party developers offer various UC applications for implementing UC systems. The various applications include Microsoft Office Communications Server (OCS), IBM Sametime (ST), Google Apps, and Cisco Jabber. Because there is no industry standard regarding UC systems, issues of incompatibility arise when one UC system needs to communicate with a different UC system. In one case, a corporation or business that employs a particular UC system may desire to communicate externally with vendors or other persons who employ a different UC system. Or in the case of internal communication, when an organization that employs a particular UC system “A” merges with another organization that employs a UC system “B”, the ability for users on system “A” to communicate with users on system “B” is often desirable. Nevertheless, the incompatibility of the UC systems often makes communication between the UC systems difficult or impossible to implement.
A system wide shift to one system can be expensive and in some cases impractical. Thus, in the past, these issues have been dealt with in a variety of ways:                1. Using multiple clients. For instance, user A would use client 1 to communicate with users on system 1 and use client 2 to communicate with users on system 2. One drawback to this system is that users who only have access to system 1 still cannot communicate with users who only have access to system 2 and vice versa.        2. Using a multi-protocol client that is capable of talking to multiple UC systems. The user still needs an account on each system.        3. Using a point federation system.        4. Switching the communication mode. That is, if IM is not possible switching to a telephone call or email.        5. Building a custom link.        
However, these alternative ways for implementing UC systems are sub-optimal as they typically result in reduced usability or in increasingly unscalable and expensive infrastructure. Furthermore, clients of two UC systems may wish to communicate with one another by media calls (e.g., audio and video calls) and/or by conference calls. However, most UC systems do not support federated calls between clients of different UC systems.